Alagille syndrome is a dominately inherited, genetic disorder characterized by bile duct paucity in combination with heart, skeletal, ocular and facial abnormalities. Multiple lines of evidence led to the suggestion that there is an Alagille Syndrome disease gene(s) on the short arm of chromosome 20 (20p12) and our group at CHOP has identified a gene within this location that we believe is the Alagille syndrome disease gene. The gene is Jagged 1, and it has been shown to be a ligand for the Notch transmembrane receptor. The Notch signaling pathway has been well studied in Drosophilia and C-elegens and acts centrally in the development of multiple organ systems. We hypothesize that loss or mutation of Jagged 1 gives rise to the characteristic spectrum of malformations seen in patients with Alagille syndrome. This study outlines a plan to: 1) Study Jagged 1 in patients with Alagille syndrome to look for mutations; 2) Study the timing and location of expression of Jagged 1 in normal human tissue through development as a first step in understanding how loss of or mutations in this gene causes Alagille syndrome; 3) Study patients whose clinical findings overlap with those of Alagille syndrome to determine if they have mutations of Jagged 1.